1. Field of Invention
In general, the present invention is directed to the interruption of a high current flowing on a high-voltage transmission line by means of a switching device known as a circuit breaker.
2. Description of Prior Art
More specifically, the object of the present invention is a puffer type liquefied-gas self-injection circuit breaker used to interrupt a high current on a high-voltage transmission line at ambient temperatures below the liquefaction temperature of the gas used.
In addition, the present invention provides for a puffer-type liquefied-gas self-injection circuit breaker comprising a device which permits the injection of liquefied gas directly on the electric arc formed at the moment of current interruption.
At the present time, there exist breaking devices of the type known as puffer circuit breakers in which the opening of the movable contact drives a compression chamber. The gases in the chamber are thereby compressed and expelled through an opening or nozzle to blast the electric arc produced between the contacts. This blasting operation produces the large mass flow rate required for extinction of the arc and interruption of the current. One advantage of this type of apparatus is that it is a "single-pressure" device and therefore does not need a high-pressure gas supply flowing into a lower-pressure chamber to supply the gas flow required for interruption, as "double-pressure" apparatus does. The breaking capacity of puffer-type breakers increases with their operating pressure and usually varies between 2 and 10 bar. However, the SF.sub.6 gas habitually used in such apparatus liquefies at low temperatures. At -50.degree. C., for example, the saturated vapor pressure is only 2.3 bar absolute whereas at -30.degree. C. it is 4.9 bar. Therefore, when the temperature drops below the liquefaction temperature, part of the gas condenses and the vapor pressure of SF.sub.6 decreases causing an almost proportional decrease in the breaking capacity. This limitation is fundamental to all these breakers, whose breaking capacity at -50.degree. C. will be about 50% of that at -30.degree. C. due to condensation.